1. Field
One or more embodiments of the present invention relate to a battery module having a plurality of batteries connected to each other.
2. Description of the Related Art
A battery module is an element of a high-capacity power supply unit formed of a plurality of batteries connected to each other and may be used as a power source for, for example, electric vehicles.
The batteries forming such a battery module are often lithium ion batteries. In a lithium ion battery, the performance thereof does not often deteriorate even if charging and discharging is repeatedly performed. However, a negative electrode of the battery may expand while lithium ions are transferred during charging. Since the battery module is formed of a plurality of lithium ion batteries connected to each other in series or in parallel, if each lithium ion battery expands a little, the entire battery module may be expanded by about 5% to about 10%. As such, the form or shape of the battery module may be excessively modified or distorted so that attaching and separating of the battery module to and from its original position may be difficult, causing electric resistance of the batteries to increase. Moreover, if the battery module is used in electric vehicles, about eight battery modules are stacked to form a battery pack to be installed in the electric vehicles. Thus, if the form of each battery module is modified, the degree of modification over the entire battery module assembly is great and thus serious problems may occur.
Accordingly, in the battery module, end plates are placed at both ends of secondary battery lines in order to suppress expansion of the secondary batteries and bar type connection rods are connected to the end plates placed at both ends of secondary battery lines, thereby fixing the end plates.
However, in general, since the connection rods and the end plates are connected to each other by using a number of bolts and nuts, it takes a relatively long time to connect them and the bolts and nuts protrude from of the battery module, thereby increasing the volume of the battery module.
An increase in the volume of the battery module causes an overall volume increase in devices employing the battery module and thus limits design of the devices. In particular, if the battery module is employed in electric vehicles, an installation space is limited and thus, if the volume of the battery module is reduced, more design flexibility is permitted.